US President is not a dictator. His (Her in the future) power is greatly limited by the congress.
President can be an important voice, but without the support from the congress, it’s meaningless.

That’s the beauty and wisdom of constitution which will ensure policy continuity and prevent dramatic change, no matter what happened.

This is a major concern for me about Obama’s presidency. To high expectation, so few “change” he can deliver. As a constitutional law professor, Obama knows this better than me.